A Theoretical Evaluation of Ultrasonic Detection of Small Gas Bubbles.
Medical research progress rept. no. 4,
NAVAL MEDICAL RESEARCH INST BETHESDA MD
Pagination or Media Count:
The scattering of ultrasound such as is commonly used in medical diagnosis by small bubbles was analyzed. A bubble larger than the acoustic wavelength casts an acoustic shadow as predicted by geometric acoustics a bubble the same size as the acoustic wavelength imparts strong directionality to the scattered wave. A bubble smaller than the acoustic wavelength radiates a scattered spherical wave of less than 0.1 of the incident energy because of dissipative losses. For a random distribution of these bubbles of sub-wavelength size the intensity of the scattered wave is directly proportional to the bubble density. A direct acoustic-optical imaging system ultrasonic Bragg imaging is insufficiently sensitive to detect bubbles smaller than an acoustic wavelength. The image detail in acoustic-optical imaging systems is limited by the acoustic wavelength, the numerical aperture of the optics, and spatially abrupt near-field acoustic intensity variations. Modified author abstract
- Acoustic Detection and Detectors
- Biomedical Instrumentation and Bioengineering